Installing Radiant Floor Heat
Radiant Heating
Photograph by Ralph Masullo
Secure the mat. Plywood or cement backerboard will work as a substrate for the heating cable. Staple into the plastic mat, not into the cable.
Trowel on the mastic. The thin profile of the cable and mat allows the cable to be easily embedded in the thinset application.
Lay the tile. Any type of tile can be installed. Complete the grout work and your floor is done.
Hydronic tubing directly under hardwood flooring. This approach does raise the floor level about 1 in., but if installed properly with nailers between the tubing it will not harm the hardwood flooring above it. The 3/4-in. layer of hardwood radiates heat to the room.
Hydronic tubing in a thin slab over wood framing. This approach is for new construction and major remodeling. Floor framing must be adequate to support the additional weight of masonry and the water pumped through the tubing.
Hydronic tubing in the joist spaces.
If you have access to joist bays beneath the floor, you can install tubing against the bottom of the subfloor for radiant heat. Insulation beneath the tubing is essential. This is the only hydronic system that doesn't require substantial remodeling.

Secure the mat. Plywood or cement backerboard will work as a substrate for the heating cable. Staple into the plastic mat, not into the cable.

Trowel on the mastic. The thin profile of the cable and mat allows the cable to be easily embedded in the thinset application.

Lay the tile. Any type of tile can be installed. Complete the grout work and your floor is done.

Hydronic Tubing Directly Under Hardwood Flooring
This approach does raise the floor level about 1 inch, but if installed properly with nailers between the tubing it will not harm the hardwood flooring above it. The 3/4-inch layer of hardwood radiates heat to the room.

Hydronic Tubing in a Thin Slab Over Wood Framing
This approach is for new construction and major remodeling. Floor framing must be adequate to support the additional weight of masonry and the water pumped through the tubing.

Hydronic Tubing in the Joist Spaces
If you have access to joist bays beneath the floor, you can install tubing against the bottom of the subfloor for radiant heat. Insulation beneath the tubing is essential. This is the only hydronic system that doesn't require substantial remodeling.

How-To Video

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How to Install Electric Radiant Heating

In this how-to video, This Old House plumbing and heating contractor Richard Trethewey explains the warming attributes of electric radiant heat

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Stepping onto ice-cold bathroom tile is a cruel way to wake up in the morning. It's no wonder so many of us invest in extra-thick slippers and giant bath mats.

But what if we were able to shed our slippers and step barefoot onto tile that's toasty warm? Radiant-floor heating makes that possible. And you can install it in your home with far less trouble and expense than you might expect.

Radiant-floor heating has been around for centuries. The principle is simple: The floor radiates heat to your feet, warming you all over. Most familiar are hydronic systems that heat your entire house. They produce wonderful heat, but they require serpentine runs of plastic tubing, water heaters or boilers, pumps and manifolds. This makes hydronic systems expensive and complicated to install.

A simpler, less expensive alternative for just a single room is one of the electric systems discussed here.

System Basics

An electric radiant system consists of thin heating cables, like the wires in an electric blanket, installed under ceramic tile. Because the cables are so thin they don't raise the level of the flooring much; this makes them great for remodeling.

They're installed where warm floors are appreciated: bathrooms, mudrooms, and kitchens. Controlled by their own thermostat, these systems don't replace your main heating unit — they augment it.

To install an electric radiant floor in an existing room, you'll need a dedicated 15- to 20-amp GFCI-protected circuit to power the system, and an excuse to lay a new tile floor. If you're remodeling, it's a good time to satisfy both requirements.

A bathroom-size warm-floor retrofit will cost $400 to $700 including the cost of the new tile. This system will consume about the same amount of electricity as three 100W lightbulbs.

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Article: Radiant Floor Heating
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